This invention relates to aerial lift platforms or cranes mounted on a mobile chassis and carrying an extendable boom.
The increasing demand for machines with greater outreach throughout 360.degree. rotation has resulted in the use of extending axles or outriggers (depending on the requirement for fully mobile or fixed base operation) to improve the stability base when the rotating upper structure is normal to the longitudinal axis of the chassis.
This has led to a problem with the steering linkage on the chassis base which has not heretofore been resolved efficiently and safely.
It is recognised with both aerial lifting platforms and cranes that when a boom on the rotating upper structure is in a position at 90.degree. to the chassis longitudinal axis, that the overturning moment of the boom together with the load lifted on the crane, or on the boom plus basket for lift platforms, reaches a maximum value because of the relative width to length of the chassis base.
Previously, improvement in operation over the side of the chassis has been achieved by the use of extending axles or extending outriggers. When it is necessary to achieve full mobility of the machine for all positions of the boom, then extending axles have been used for the purpose.
To utilise extending axles efficiently, the steering geometry and linkage must compensate for the change in position of the wheels owing to the axle extension.
Previously this has been achieved with the use of a large number of components and consequently some of the bracketry has been positioned forward of the axle in a vulnerable position which could affect the safety of the machine.
Steering linkage which may be telescopic is normally held in position, at its minimum and maximum extension, by pins located at suitable positions in the drag rods.